Anaesthesia enables the painless performance of medical procedures that would otherwise cause severe or intolerable pain to an unanaesthetized patient. Three broad categories of anaesthesia exist:

• General anaesthesia suppresses central nervous system activity and results in unconsciousness and total lack of sensation.
• Sedation suppresses the central nervous system to a lesser degree, inhibiting both anxiety and creation of long-term memories without resulting in unconsciousness.
• Regional anaesthesia and local anaesthesia, which block transmission of nerve impulses between a targeted part of the body and the central nervous system, causes loss of sensation in the targeted body part. A patient under regional or local anaesthesia remains conscious, unless general anaesthesia or sedation is administered at the same time.